Patterning media is used in a variety of technologies for providing storage of data, processing, and other functionality to electronic and magnetic devices. Patterning techniques are employed to spatially define features having different electrical or magnetic properties. Moreover, patterning techniques are used as part of the fabrication process for building a wide variety of semiconductor and magnetic devices.
Patterned features in magnetic media are used for storing digital data that can be erased and rewritten. Patterned magnetic media is used in memory devices, such as MRAM and magnetic logic, and is being developed for use in storage devices, such as disk or tape drives. Patterned magnetic media on a disk or tape substrate can be referred to as bit-patterned magnetic media. In patterned magnetic media for storage devices, some of the patterned features are designed as storage elements of digital bits of data and other patterned features are designed for functions, such as providing servo information to position a read/write head.
Several techniques are known for patterning bit-patterned magnetic media. Prior techniques relied on an etching process for forming the patterns of storage elements in data storage media. However, such techniques required the planarization of the etched disk, which can result in increased cost and labor, as well as a reduction in yield. Accordingly, recently there has been a desire to develop certain techniques to mitigate the shortcomings of etching-based processes. For example, masked ion-beam and masked plasma immersion ion implantation lithography has proven to be an efficient alternative for producing patterned media.
One masked ion-beam lithography approach for relatively low areal density patterned media employs a stencil mask for defining the pattern on a medium (e.g., a resist-covered semi-conductor wafer). The stencil mask is made of a silicon wafer placed in an elevated position above the medium. The wafer includes a series of openings corresponding to the desired pattern to be formed on the medium. A lithography beam made of energetic ions traverses through the openings of the stencil mask and is incident onto the medium to transfer the stencil pattern to the medium.
Another masked ion-beam lithography approach for relatively high areal density patterned media utilizes a hard mask applied to a medium (e.g., a semi-conductor wafer or a magnetic storage disk). A pattern, including a series of openings, is formed in the hard mask using known etching techniques. Once the pattern is formed, a beam of energetic ions is directed through the openings in the hard mask onto an exposed layer of the medium. The energetic ions impacting the medium alter the properties of the exposed layer to form a series of patterns in the medium corresponding to the pattern of the hard mask. The patterns can have a variety of sizes and shapes.
Similar to ion-beam lithography, plasma immersion ion implantation techniques form energetic ions which traverse through openings in a hard mask applied on a medium to be patterned. However, unlike ion-beam lithography, plasma techniques form the energetic ion species via a plasma medium as opposed to a directed ion beam.
Masked ion implantation techniques introduce a substantial amount of energetic ions onto the patterned mask. Based on the ion species used, the energetic ions tend to erode or sputter-etch the mask, which results in a reduction in the thickness of the mask. One negative consequence of reducing the thickness of the mask is that at a certain thickness, the mask fails to effectively block or stop the energetic ions. Unblocked energetic ions passing through the mask impact the medium at undesirable locations to negatively alter the intended pattern on the medium and render the medium unusable. Exacerbating this shortcoming is the push to extend the resolution of the ion implant process to enable higher areal densities, particularly with patterned magnetic media, by reducing the lateral straggle of the ion species used for implantation. The most promising approach for reducing lateral straggle is to increase the mass of the energetic ion species. However, such higher mass ion species tend to sputter etch the mask at a higher rate for a given ion dosage, which results in a higher rate of mask thickness reduction.
Further, the trending of increased areal density of, and the corresponding reduction in size of, storage elements or features on a medium demands that mask thickness be designed with smaller thickness to accommodate the correspondingly increased density of bit patterns on the mask. Therefore, to achieve higher areal densities, the erosion of masks due to ion sputtering must be carefully and precisely controlled.
Similar to patterned magnetic media, electronic devices, such as semiconductor devices, utilize ion implantation techniques for forming a pattern of doped regions in a medium exposed to energetic ions via apertures formed in a hard mask applied to the medium. The implanted ions cause the electrical properties of the doped regions in the medium to change from an initial value of the medium (e.g., semiconductor medium), thereby leaving un-doped regions covered by the hard mask between the doped regions.
In the past, when electrical devices were large in size and doping densities were low, building hard masks that were adequately robust to hold up against etching by the energetic ions was fairly straightforward. However, as the number of devices on a chip has increased, the characteristic sizes of the devices have correspondingly decreased, both laterally and in thickness. Correspondingly, the thickness and distances between adjacent apertures of the hard mask have been constrained to be reduced, which results in a reduction in the mechanical strength of the mask. Moreover, as electrical devices on a chip become thinner, the ion implantation depth is decreased to efficiently implant the ions substantially within the target medium thickness. Accordingly, the energy of the implanting ions must be adjusted so they stop within the thickness of the media. Generally, adjustment of the energy of the implanting ions is accomplished by lowering the energy of the implanting ions. However, one undesired byproduct of lowering the energy of the implanting ions is that the sputter yield of the implanting ions increases, which tends to increase the erosion of the hard mask for a given number of implanting ions. Further, because recently developed ion implantation tools have helped facilitate an increase in implant current density, building devices with relatively high implant dosages (e.g. 1015˜1016 ions/cm2) is now possible. But, the higher the implant dosages, the greater the undesired erosion of the hard mask. Thus, as electronic devices, such as semiconductor devices, shrink in size, it will be necessary to employ thinner hard masks that adequately stop a larger number of ions generating a higher number of sputtered mask atoms.
Current ion implantation techniques for forming patterned media fail to adequately control the erosion of patterned masks. For example, some techniques reinforce the mask with a coating prior to the ion implantation process. However, the coating can still be eroded with use of some ion species. Some stencil mask techniques attempt to compensate for energetic ion-caused sputtering of the mask by depositing material to the mask and subsequently sputtering the newly deposited material. The subsequent sputtering is required to reduce deviations from homogeneity necessarily present in the deposited material. Without the subsequent sputtering step, the newly deposited material would not be homogenous, which can reduce the effectiveness of the stencil mask. Accordingly, not only is this deposition and sputtering technique limited to ion implantation processes that use stencil masks, as opposed to hard mask coatings, but it requires an additional sputtering step, which increases manufacturing costs and time. Additionally, because ion implantation processes using stencil masks are limited to low areal density samples, no known techniques are available for compensating for the energetic ion-caused erosion of hard masks in the production of high areal density samples.